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SubjectRe: [PATCH v2 2/2] nvmem: Add Apple eFuse driver


On Sun, Mar 6, 2022, at 13:25, Krzysztof Kozlowski wrote:
> On 06/03/2022 13:18, Sven Peter wrote:
>> Apple SoCs contain eFuses used to store factory-programmed data such
>> as calibration values for the PCIe or the Type-C PHY. They are organized
>> as 32bit values exposed as MMIO.
>>
>> Signed-off-by: Sven Peter <sven@svenpeter.dev>
>> ---
>> v1 -> v2:
>> - fixed sparse warning about __iomem by introducing
>> struct apple_efuses_priv as done in other nvmem drivers
>> - make sure the driver actually works as a module by
>> setting .owner to THIS_MODULE and adding MODULE_DEVICE_TABLE
>> pointed out by Joey Gouly
>>
>> MAINTAINERS | 1 +
>> drivers/nvmem/Kconfig | 12 ++++++
>> drivers/nvmem/Makefile | 2 +
>> drivers/nvmem/apple-efuses.c | 82 ++++++++++++++++++++++++++++++++++++
>> 4 files changed, 97 insertions(+)
>> create mode 100644 drivers/nvmem/apple-efuses.c
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index f70d8525cbd4..e3e973a3f651 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -1781,6 +1781,7 @@ F: drivers/i2c/busses/i2c-pasemi-core.c
>> F: drivers/i2c/busses/i2c-pasemi-platform.c
>> F: drivers/irqchip/irq-apple-aic.c
>> F: drivers/mailbox/apple-mailbox.c
>> +F: drivers/nvmem/apple-efuses.c
>> F: drivers/pinctrl/pinctrl-apple-gpio.c
>> F: drivers/soc/apple/*
>> F: drivers/watchdog/apple_wdt.c
>> diff --git a/drivers/nvmem/Kconfig b/drivers/nvmem/Kconfig
>> index da414617a54d..bba29d1aec96 100644
>> --- a/drivers/nvmem/Kconfig
>> +++ b/drivers/nvmem/Kconfig
>> @@ -300,4 +300,16 @@ config NVMEM_BRCM_NVRAM
>> This driver provides support for Broadcom's NVRAM that can be accessed
>> using I/O mapping.
>>
>> +config NVMEM_APPLE_EFUSES
>> + tristate "Apple eFuse support"
>> + depends on ARCH_APPLE || COMPILE_TEST
>> + default ARCH_APPLE
>> + help
>> + Say y here to enable support for reading eFuses on Apple SoCs
>> + such as the M1. These are e.g. used to store factory programmed
>> + calibration data required for the PCIe or the USB-C PHY.
>> +
>> + This driver can also be built as a module. If so, the module will
>> + be called nvmem-apple-efuses.
>> +
>> endif
>> diff --git a/drivers/nvmem/Makefile b/drivers/nvmem/Makefile
>> index dcbbde35b6a8..1a8e54691d3e 100644
>> --- a/drivers/nvmem/Makefile
>> +++ b/drivers/nvmem/Makefile
>> @@ -61,3 +61,5 @@ obj-$(CONFIG_NVMEM_RMEM) += nvmem-rmem.o
>> nvmem-rmem-y := rmem.o
>> obj-$(CONFIG_NVMEM_BRCM_NVRAM) += nvmem_brcm_nvram.o
>> nvmem_brcm_nvram-y := brcm_nvram.o
>> +obj-$(CONFIG_NVMEM_APPLE_EFUSES) += nvmem-apple-efuses.o
>> +nvmem-apple-efuses-y := apple-efuses.o
>> diff --git a/drivers/nvmem/apple-efuses.c b/drivers/nvmem/apple-efuses.c
>> new file mode 100644
>> index 000000000000..dd5576ec5408
>> --- /dev/null
>> +++ b/drivers/nvmem/apple-efuses.c
>> @@ -0,0 +1,82 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * Apple SoC eFuse driver
>> + *
>> + * Copyright (C) The Asahi Linux Contributors
>> + */
>> +
>> +#include <linux/io.h>
>> +#include <linux/mod_devicetable.h>
>> +#include <linux/module.h>
>> +#include <linux/nvmem-provider.h>
>> +#include <linux/platform_device.h>
>> +
>> +struct apple_efuses_priv {
>> + void __iomem *fuses;
>> +};
>> +
>> +static int apple_efuses_read(void *context, unsigned int offset, void *val,
>> + size_t bytes)
>> +{
>> + struct apple_efuses_priv *priv = context;
>> + u32 *dst = val;
>> +
>> + while (bytes >= sizeof(u32)) {
>> + *dst++ = readl_relaxed(priv->fuses + offset);
>> + bytes -= sizeof(u32);
>> + offset += sizeof(u32);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int apple_efuses_probe(struct platform_device *pdev)
>> +{
>> + struct apple_efuses_priv *priv;
>> + struct resource *res;
>> + struct nvmem_config config = {
>> + .dev = &pdev->dev,
>> + .read_only = true,
>> + .reg_read = apple_efuses_read,
>> + .stride = sizeof(u32),
>> + .word_size = sizeof(u32),
>> + .name = "apple_efuses_nvmem",
>> + .id = NVMEM_DEVID_AUTO,
>> + .owner = THIS_MODULE,
>> + .root_only = true,
>> + };
>> +
>> + priv = devm_kzalloc(config.dev, sizeof(*priv), GFP_KERNEL);
>> + if (!priv)
>> + return -ENOMEM;
>> +
>> + priv->fuses = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
>> + if (IS_ERR(priv->fuses))
>> + return PTR_ERR(priv->fuses);
>> +
>> + config.priv = priv;
>> + config.size = resource_size(res);
>> +
>> + return PTR_ERR_OR_ZERO(devm_nvmem_register(config.dev, &config));
>> +}
>> +
>> +static const struct of_device_id apple_efuses_of_match[] = {
>> + { .compatible = "apple,efuses", },
>> + {}
>> +};
>> +
>> +MODULE_DEVICE_TABLE(of, apple_efuses_of_match);
>> +
>> +static struct platform_driver apple_efuses_driver = {
>> + .driver = {
>> + .name = "apple_efuses",
>> + .of_match_table = apple_efuses_of_match,
>> + .owner = THIS_MODULE,
>
> You wrote it also in changelog, but why do you need it? Doesn't core set
> it? Coccinelle should complain about this as well.
>

yeah, you're right. I shouldn't have just blindly followed what Hector and Joey
had to do for another subsystem to make reference counting work there.

I just checked again and it's neither required here not in struct nvmem_config
because module_platform_driver -> platform_driver_register ->
__platform_driver_register will set it in struct platform_driver and the
nvmem core will take it from there and set it inside nvmem_config.


thanks,


Sven

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